Start by breaking the glaze. An automatic centre-punch is excellent for this. Then use a masonry bit, rotated fairly slowly, without hammer action - but lean on the drill to generate quite a lot of pressure.
Only when it's easy to replace the tile though ! (ideally before setting the tile on the wall). Do a dozen holes this way and there's a real risk of cracking at least one tile.
I find tiles pretty easy to drill and the trick is to use a sharp tile or glass bit, not a masonry bit. This is a carbide "leaf" bit and it has a sharp cutting edge, unlike a masonry drill that's just a blunt chisel. You will need to lean on the bit with plenty of force to get through that initial glaze.
Oh, and tape the hammer selector on your drill firmly into the "off" position. It's even worth using two drills here, or drilling in two batches, non-hammer to drill the tiles, then switching to hammer to drill the wall behind. Switching over for each hole is a bad idea - one time you'll forget to switch back. If you touch a tile with the drill in hammer mode, then you'll crack it (yes, I've done it).
He's talking about 'A tile' here, a tile that you'd swear it was mixed with iron filings and granite. I know the trouble he's having and I've been there and that was only one tile I had to drill. The way I done it was to drill a pilot hole first with a sharp masonary bit(10 minutes later) I put a carborundum bit in the right size for the hole and put my drill in rotary hammer action applied oil periodically and slowly applied pressure it was drilling and chamfering and took me a good 20 minutes to get three quaters of the way throught the damn thing, I then turned the tile over to complete the cut because there was a chance of cracking the tile had I not turned it over.
I've just had the bathroom tiled with porcelain tiles. I think the secret is to drill small pilot holes first with a glass cutting bit, then use a larger glass bit. The tiles were drilled after being laid. There'll be more holes drilled tomorrow. I'm hoping that it goes smoothly.
I would probably not have chosen these tiles if i knew what a hassle they'd cause. I understand that another customer tried to take the tile shop to court after she used a bath cleaner on the tiles and they reacted. I've been warned in no uncertain terms never to let anything acidic near them.
Normal tiles are easy - break the glaze and anything works. Fully vitrified ones are a different kettle of fish, my tiler neighbour uses diamond faced drill bits on them. Normal masonry drills simply crack them and HS drills have no effect. I will ask him for any other ideas tomorrow!
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